Lithium carbonate has been used for various applications such as a compounding agent of heat-resistant glass, optical glass and the like, a ceramic material, a raw material of lithium secondary batteries used as batteries of cellular phones and notebook computers, a material of electrolytes, and a raw material of lithium niobate single crystals and lithium tantalate single crystals used in semiconductor lasers and the like.
Characteristics required for the lithium carbonate are variable and vary according to its application. For example, when lithium carbonate is used as the above-mentioned electronic materials or optical industrial materials, a large amount of impurities deteriorate electric properties or optical properties thereof. It is therefore required to contain less impurities and have a high purity. Further, as the raw material of lithium secondary batteries, there has been demanded lithium carbonate having a purity of 97% or more, preferably 98% or more, more preferably 99% or more and still more preferably 99.5% or more. In addition, high purity lithium carbonate in which the content of dissimilar metals and the other impurities is at a level of several ppm and further 1 ppm or less is demanded in some cases.
The lithium carbonate is produced from naturally-occurring lithium resources, and as the resources in which such lithium occurs in high concentrations and in large amounts, there are lithium deposits and brines in intercontinental salt lakes. In the present situation, however, the production of lithium carbonate using the brines in intercontinental salt lakes constitutes a large proportion thereof (see Non-Patent Documents 1 and 2).
Further, for the production from the brines, with advance of development of electric vehicles, lithium batteries have been in the limelight as driving force sources, and attention has been attracted to the brines as the lithium resources again, as supply sources for large consumption thereof (see Non-Patent Documents 1 and 2).
The salt lakes in which the brines are obtained are in limited areas such as China, U.S.A., Chile, Argentine and Bolivia, and unevenly distributed.
In particular, salt lakes in the Andean area such as Salar de Atacama (Chile), Salar de Hombre Muerto (Argentine) and Salar de Uyuni (Bolivia) are excel at their lithium reserves (see Non-Patent Document 1). Actually, a large amount of lithium carbonate is produced using the brines in this area as raw materials of lithium (see Non-Patent Document 2).
The concentration of lithium (Li) in the brines of these salt lakes in the Andes is about 0.05 to 0.3%. After concentrated to about 6% in the sun, this is utilized for the above-mentioned production of lithium carbonate and the like. In that case, this is utilized for the production of lithium carbonate and the like, in a form of lithium chloride.
In these brines, there are contained sodium, potassium, magnesium and the like in high concentrations, in addition to lithium, and in order to produce high purity lithium carbonate, it is necessary to separate and remove these components. Also in the conventional art, these components are removed before or after a carbonation reaction.
With respect to the lithium carbonate, high purity lithium carbonate is demanded as described above, and it is also as described above that lithium carbonate containing 1 ppm or less of impurities is demanded in some cases.
Methods for producing such high purity lithium carbonate include, for example, a method of subjecting to microfiltration an aqueous solution containing lithium bicarbonate obtained by reacting crude lithium carbonate with carbon dioxide, and thereafter, subjecting the aqueous solution containing lithium bicarbonate to heat treatment to precipitate lithium carbonate (see Patent Document 1), and a method of treating with an ion-exchange module an aqueous solution containing lithium bicarbonate obtained by reacting crude lithium carbonate with carbon dioxide, and thereafter, subjecting the lithium bicarbonate-containing aqueous solution to heat treatment to precipitate lithium carbonate (see Patent Document 2).
Patent Document 1: JP-A-62-252315
Patent Document 2: JP-T-2002-505248
Non-Patent Document 1: GSJ Chishitsu News No. 670, pages 22 to 26, “Lithium Resources”
Non-Patent Document 2: GSJ Chishitsu News No. 670, pages 49 to 52, “Production of Lithium from Salar de Atakama, Chile, and Use of Lithium Compounds”